1. Field of the Invention
This invention is in the field of methods and apparatus used in pre-screening to prevent entry of ferromagnetic threat objects into the vicinity of a magnetic resonance imaging (MRI) magnet.
2. Background Art
Even small ferromagnetic objects that are inadvertently carried into a magnetic resonance imaging examination room can become potentially lethal projectiles in the very high field and high field gradient surrounding the MRI magnet. Large ferromagnetic objects, such as oxygen tanks, floor scrubbers, tables, and pipe wrenches pose threat of great harm to patients undergoing MRI, as well as damage to the MRI instrument itself. Such objects are called “ferromagnetic threat objects” herein. A terrible accident occurred to a small boy when an oxygen tank was inadvertently brought into the magnet room, causing his death. Many “near-misses” have occurred, and most MRI centers can relate such potentially-dangerous incidents.
Oxygen tanks are painted green by convention, thus heightening the illusion that these are safe in a magnetic resonance environment, which is absolutely untrue. What is needed, then, is a way of ensuring that oxygen tanks, floor scrubbers, and other ferromagnetic threats are not brought into the magnet room under any circumstances. The present invention provides a method and apparatus for this purpose.